Limiting Light Escape Angle in Silicon Photovoltaics: Ideal and Realistic Cells

Abstract

Restricting the light escape angle within a solar cell significantly enhances light trapping, resulting in potentially higher efficiency in thinner cells. Using an improved detailed balance model for silicon and neglecting diffuse light, we calculate an efficiency gain of 3% ab s for an ideal Si cell of 3-μm thickness and the escape angle restricted to 2.767°under AM1.5 direct illumination. Applying the model to current high-efficiency cell technologies, we find that a heterojunction-type device with better surface and contact passivation is better suited to escape angle restriction than a homojunction type device. In these more realistic cell models, we also find that there is little benefit gained by restricting the escape angle to less than 10°. The benefits of combining moderate escape angle restriction with low to moderate concentration offers further efficiency gains. Finally, we consider two potential structures for escape angle restriction: a narrowband graded index optical multilayer and a broadband ray optical structure. The broadband structure, which provides greater angle restriction, allows for higher efficiencies and much thinner cells than the narrowband structure.

Concepts for external light trapping and its utilization in colored and image displaying photovoltaic modules

“…Moreover, because of the optical recycling, thinner solar cells can be used which benefit from lower Auger and (bulk) Shockley-Read-Hall charge-carrier recombination, which results in a higher open circuit voltage (V oc ). Thereby, the theoretical efficiency limit of this type of angular restriction is significantly higher than that of cells without angular restriction [1,6].…”

“…There has been significant interest in angular confinement for solar energy by many authors using rugate filters, interference filters, and light confining cavities to address the aforementioned issues [1][2][3][4][5][6][7][8]. State-of-the-art rugate filters and interference filters enable wavelength and angular selective transmission (and reflection) based on interference due to Fresnel reflection in their refractive index profile.…”

Computer calculations across time and length scales in photovoltaic solar cells

“…Alternative LM strategies include luminescent solar concentrators that absorb and selectively re-emit light in the active layer, 178 or nanostructures able to restrict the light emission angle to potentially reduce entropy losses due to light emission. 28,179 Computational methods available to study LM at the nm-mm scale focus on computing the electromagnetic field within the active layer by solving Maxwell's equations. Among different possible implementations, a popular choice is finite-difference time-domain (FDTD) simulations propagating Maxwell's equation in time using real-space grids.…”

Broadband angular selectivity of light at the nanoscale: Progress, applications, and outlook

“…For solar cells with diffusive back reflector (Fig. 9A) [75], it has been theoretically shown that limiting the emission angle in the solar spectrum can reduce the optical escape cone and enhance the light trapping [31,65,76,77]. Enhanced light trapping effect allows for better absorption of sunlight in a very thin cell (reducing material usage), and an increase in current, voltage and efficiency of the solar cell as well.…”